An endodontic post for the purposes of this invention is to be considered as made of metal. This post at its distal end is inserted into a properly prepared root canal opening and approximates to about 1 mm. of the apex of the tooth. It is secured in place by highly polar cementitious substances such as a zinc oxide-eugenol composition, a zinc phosphate composition and the like, and in addition with non-polar compositions such as gutta percha which is a trans isomer of polyisoprene.
At the coronal end the post serves as a foundation or as an anchoring pin for a superposed composite generally comprising a room-temperature setting mixture of precursor prepolymer and a catalyst in a soft plastic consistency of about 70,000 centipoises before hardening in situ.
The metal post is galvanically affected by the strongly reactive environment coupled with the strongly reactive fluids in the mouth and strongly reactive bacterial breakdown products. And in addition the metal post is constantly being abraded and the surface ions sloughed off and donated to its circumambient securing cementitious compositions, weakening same. This abrasion takes place by the the minute movements of the metal post due to mastication and mouth-movements.
In the case of metal posts made of silver, corrosion and secondary decay universally occurred after about six years or perhaps sooner. The patient had a pain, a swelling and a full abscess within the root canal. The decayed tooth has now to be removed along with the erstwhile expensive restoration. More expensive dental and prosthetic procedures are now called for including partial pontics, dentures and the like.
While silver posts are now in disuse, other metal posts are used and these are generally made of stainless steel, of a non magnetic type 404 or the like. The stainles steel alloy must be capable of ductility, machinability, casting and other metal fabrication techniques. While the stanless steel alloy is not as reactive as silver, it is still reactive, and surface layers of ions are sloughed off and interact with the root-canal compositions and with the seepage of bacterial products from the oral cavity. Furthermore the surface of the metal posts described is further mechanically abraded by the constant imperceptible movements within the root canal cavity and the abrasive action of the cements surrounding it and seeking to impede its movements, and to impair lodgement of the post after implantation. The object of this invention therefore is to provide a metal post of extreme passivity and extreme hardness.
The hardness is imparted to the surface of the novel metal post by ion implantation, chemical passivity is similarly imparted.
To achieve these and other objects of the invention an ion layer is donated to the surface of the metal post achieving a surface character not possible by plating or coating and a hardness not possible by casting or machining.
The metal post hereinafter referred to as the endodontic post is surface-implanted with a layer of ions derived from a metal that is harder than the metal comprising the main body of the post. In addition the surface layer of ions is comprised of a metal that has greater chemical passivity than the metal comprising the main body of the post. Typically the surface ion layer will be nitrogen. Chemical passivity means corrosion resistance as related to the composites, the securing chemical compositions, the oral fluids, the bacterial breakdown products from materials in the mouth of the patient.